The present invention relates to a novel chromogenic compound, color developing composition containing the same suitable for recording paper, and pressure- or heat-sensitive recording paper coated with microcapsules containing the color developing composition.
Heretofore, a variety of yellow color forming agents have been proposed and they are broadly clasified into the following two groups.
Group I: Those having a lactone ring in the molecule.
(i) Fluoran derivatives such as 3,6-dialkoxyfluoran (refer to Japanese Patent Publication Nos. 45-4698 (1970) and 46-16053 (1971)) and 3-N-alkylaminofluoran (refer to Japanese Patent Publication Nos. 46-22650 (1971) and 48-4051 (1973)).
(ii) Chromenopyrazole compounds (refer to Japanese Patent Publication No. 46-23513 (1971)).
(iii) Aminophthalide compounds (refer to Japanese Patent Application Laying-Open (KOKAI) No. 54-111528 (1979)).
(iv) Acyloxytetrachlorophthalide compounds (refer to Japanee Patent Publication No. 45-25654 (1970)).
Group II: Those having no lactone ring in the molecule.
(i) Spiropyran derivatives (refer to Japanese Patent Publication Nos. 46-10075 (1971) and 46-11113 (1971)).
(ii) Styryl compounds (refer to Japanese Patent Publication Nos. 41-21033 (1966) and 51-27169 (1976)).
(iii) Pyridine derivatives (refer to Japanese Patent Publication No. 53-9127 (1978)).
(iv) Monomethine compounds (refer to Japanese Patent Application Laying-Open (KOKAI) No. 52-23406 (1977) and Japanese Patent Publication No. 49-5929 (1974)).
(v) Benzopyran compounds (refer to Japanese Patent Publication No. 56-19274 (1981)).
The compounds belonging to Group I which have a lactone ring in the molecule have an advantage of being less liable to spontaneous color formation in case of coating the solution thereof with a paper and being readily soluble in solvents. However, they also have a disadvantage of giving rise to a color image which is poor in color density and light-fastness.
On the other hand, the compounds belonging to Group II which have no lactone ring in the molecule have an advantage of producing a color image which is good in color density and light-fastness. However, they also have a disadvantage of being poor in solubility, being liable to spontaneous color formation in case of contact with paper, and being readily lost by sublimation.
Previously to the present invention, two of the present inventors as a part of inventors completed an invention relating to:
(1) a chromogenic compound of the formula ##STR2## wherein R.sup.1 and R.sup.2 independently represent a hydrogen atom, lower alkyl group of 1 to 5 carbon atoms, lower alkoxy group of 1 to 5 carbon atoms, or halogen atom; R.sup.3 represents a hydrogen atom, alkyl group of 1 to 12 carbon atoms, alkoxyalkyl group of 1 to 12 carbon atoms, halogenoalkyl group of 1 to 12 carbon atoms, phenyl group which may be substituted, or benzyl group which may be substituted; and m and n are an integer of 1 or 2; providing that R.sup.1 and R.sup.2 do not represent a hydrogen atom, methyl group, and methoxy group when R.sup.3 represents a hydrogen atom or methyl group;
(2) a color forming composition for a recording material, comprising at least one chromogenic compound as defined above which is capable of developing a color upon contact with an electron acceptor; and
(3) pressure- or heat-sensitive recording paper comprising microcapsules containing at least one chromogenic compound as defined above, said chromogenic compound functioning as a color former and being dissolved in an organic solvent in said microcapsules (Refer to G.B. Pat. No. 2136823A and U.S. patent application No. 580,604 filed on Feb. 16, 1984.).
The present inventors carried out studies for obtaining a new chromogenic compound which is easier to synthesize and more soluble than the one disclosed in the previous publications mentioned above, and as a result, it is found that a chromogenic compound of the formula (I): ##STR3## wherein R represents an alkyl group of 6 to 12 carbon atoms or benzyl group, and ring A and ring B in the quinolyl group may be substituted is easy to synthesize, is readily soluble, and stable to light, and in addition, develops a color image of deep hue. On the basis of the findings the present invention has been attained.